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Chapter 3

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  1. Chapter 3 Geology of the Oceans © 2006 Thomson-Brooks Cole

  2. World Ocean • Primitive earth and formation of the ocean • early earth thought to be composed of silicon compounds, iron, magnesium oxide, and other elements • gradually, the earth heated, causing melting and separation of elements • water vapor locked within minerals released to the surface, where it cooled, condensed, and formed the ocean © 2006 Thomson-Brooks Cole

  3. World Ocean • Ocean and the origin of life • atmosphere formed by gases escaping from the planet • no accumulation of oxygen until evolution of photosynthesis—free oxygen forms oxides • Stanley Miller’s apparatus © 2006 Thomson-Brooks Cole

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  6. World Ocean • The ocean today • 4 major ocean basins: Pacific, Atlantic, Indian and Arctic • seas and gulfs © 2006 Thomson-Brooks Cole

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  9. Continental Drift • Layers of the earth • solid inner core—iron- and nickel-rich • liquid outer core (same composition) • mantle—thickest layer with greatest mass, mainly magnesium-iron silicates • crust—thinnest and coolest, outermost © 2006 Thomson-Brooks Cole

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  12. Continental Drift • Moving continents • Alfred Wegener • Pangaea, Laurasia and Gondwanaland © 2006 Thomson-Brooks Cole

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  14. Continental Drift • Forces that drive continental movement • magma convection currents • midocean ridges form along cracks where magma breaks through the crust • at subduction zones, old crust sinks into the mantle where it is recycled • seafloor spreading causes continental drift © 2006 Thomson-Brooks Cole

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  17. Continental Drift • Evidence for continental drift • fit of continental boundaries • earthquakes • seafloor temperatures highest near ridges • age of crust, as determined by samples drilled from the ocean bottom, increases with distance from a ridge © 2006 Thomson-Brooks Cole

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  21. Continental Drift • Theory of plate tectonics • lithosphere is viewed as a series of rigid plates separated by earthquake belts • divergent plate boundaries—midocean ridges where plates move apart • convergent plate boundaries—trenches where plates move toward each other • faults—regions where plates move past each other (e.g. transform faults) • rift zones—where lithosphere splits © 2006 Thomson-Brooks Cole

  22. Continental Drift • Rift communities • depend on specialized environments found at divergence zones of the ocean floor • first was discovered by Robert Ballard and J.F. Grassle in 1977, in the Galápagos Rift • primary producers are chemosynthetic bacteria © 2006 Thomson-Brooks Cole

  23. Ocean Bottom • Continental margins • continental shelf, continental slope, and shelf break • submarine canyons and turbidity currents • continental rises • shaping the continental shelves • glaciers • sediments © 2006 Thomson-Brooks Cole

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  29. Ocean Bottom • Ocean basin • abyssal plains and hills • seamounts • ridges and rises • trenches and island arcs • Life on the ocean floor • continental shelves are highly productive • life on the abyssal plains is not abundant owing to the absence of sunlight © 2006 Thomson-Brooks Cole

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  33. Composition of the Seafloor • Sediment—loose particles of inorganic and organic material © 2006 Thomson-Brooks Cole

  34. Composition of the Seafloor • Hydrogenous sediments • formed from seawater through a variety of chemical processes • e.g. carbonates, phosphorites • Biogenous sediments • formed from living organisms • mostly particles of corals, mollusc shells, shells of planktonic organisms © 2006 Thomson-Brooks Cole

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  36. Composition of the Seafloor • Terrigenous sediments • produced from continental rocks by the actions of wind, water, freezing, thawing • e.g. mud (clay + silt) • Cosmogenous sediments • formed from iron-rich particles from outer space which land in the ocean and sink to the bottom © 2006 Thomson-Brooks Cole

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  38. Finding Your Way around the Sea • Maps and charts • Mercator projections • bathymetric charts • physiographic charts © 2006 Thomson-Brooks Cole

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  42. Finding Your Way around the Sea • Reference lines • latitude • longitude • divisions of latitude and longitude © 2006 Thomson-Brooks Cole

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  45. Finding Your Way around the Sea • Navigating the ocean • principles of navigation • a sextant was used to determine latitude based on the angle of the North Star with reference to the horizon • longitude determined using chronometer © 2006 Thomson-Brooks Cole

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  47. Finding Your Way around the Sea • Navigating the ocean • global positioning system (GPS) • utilizes a system of satellites to determine position • GPS measures the time needed to receive a signal from 3 satellites, and calculates position © 2006 Thomson-Brooks Cole

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  49. Key Concepts • The world ocean has four main basins: the Atlantic, Pacific, Indian, and Arctic. • Life first evolved in the ocean. • The earth’s crust is composed of moving plates. • New seafloor is produced at ocean ridges and old seafloor is removed at ocean trenches. © 2006 Thomson-Brooks Cole

  50. Key Concepts • The ocean floor has topographical features similar to those found on continents. • The seafloor is composed of sediments derived from living as well as nonliving sources. • Latitude and longitude determinations are particularly necessary for precisely locating positions in the open sea, where there are no features at the surface. © 2006 Thomson-Brooks Cole